I'm new to 1/8 buggies, but I can say something about the O.S. engine. I put one into my XTM to replace the stock .247 engine that was in it. The .247 was a beast. It really hauled, but it died on me, so I got the O.S. I will say that it isn't the fastest and it doesn't produce the most horse power, but it does have more than adequate horsepower and it has enough top end to be competitive on a tight track.

I can also say that I don't think that I'll ever go out and buy a new engine that isn't made by O.S., if all of them are made like the RG. I have the "X" version with the pull start. Tuning is VERY easy and it holds it. Starting is also VERY easy. This thing has been the least tempermental engine I've ever messed with. If you want all out performance, then go for the hyper. If this is going to be your only engine for now and you want dependability and ease of running, go for the O.S.